Method of printing security code

ABSTRACT

A method of printing a security code on an article includes applying droplets of an ink composition with an ink jet printer to a surface of an article to print an encrypted code. The ink composition includes an organic solvent, a binder resin, and a luminescent dye.

BACKGROUND OF THE INVENTION

The present disclosure relates to the use of ink containing luminescentdyes for machine readability and/or security applications.

There is a need for many products to include a machine readable code ormark. Existing online printing systems are either too costly toimplement or are too unreliable due to several key aspects. First, themachine readable or security code is applied at high speed directlyonto, for example, mail envelopes or the packaging material of consumergoods and then needs to be subsequently read with high precision andrepeatability to be verified online by the system. Camera-based readingsystems are often employed in the verification of such codes becausethey are relatively inexpensive and can be easily adapted to readvarious code symbologies. As the case with any digitally interpretedimage, cameras require a certain dwell time (or acquisition time) overthe printed code when attempting to acquire the digital image that isused to decipher and analyze the code therein. The printing backgroundmay be highly variable (e.g., including multiple colors) with both lightand dark regions. The dark and light regions interfere with what wouldotherwise be a coherent light pattern emitted from the surface. Forexample, the light regions artificially amplify the light that thecamera sees and, conversely, light is attenuated by the dark regions.For these reasons, it is often difficult, especially at high speed, foran automated system to decipher these codes.

Printed codes from luminescent inks are illuminated by an excitationlight source with a given wavelength range and spontaneously emit lightat a second wavelength range. The fact that light is actively emittedfrom the surface and travels directly back to the camera allows for agreater imaging contrast between the printed code and the background aswhen compared with, for example, a merely light absorbing mark,especially at rapid acquisition rates. For example on a high speedproduction line (i.e., up to about 1000 feet per minute) an item mayspend a small amount of time within a camera's field of focus. There isgenerally a need for bright luminescent inks that solve these high speedmachine readable applications.

For machine readable applications and particularly securityapplications, there is often a need for the print codes to be durableand to survive environmental conditions for a predetermined life-spanafter printing. Fluorescent or phosphorescent pigmented inks are oftenselected for these applications based on their insolubility, water andlightfastness.

There are downsides to using luminescent pigments instead of dyes formachine readable applications. For example, fluorescent pigmentsgenerally exhibit reduced fluorescence as compared to fluorescent dyes.Reduced fluorescent intensity reduces the reader's ability to verify theprinted code on a high speed production line. Current approaches thatrely on pigments are also less reliable due to problems associated withrunning pigmented inks reliably in inkjet printers. The inks and systemsof this invention lend toward better system uptime, good print quality,verifiability at high speed with camera systems, good water resistanceand relatively good light stability.

The needs as outlined above apply to several specific applicationsincluding black market security applications, grey market or diversionprevention, producer authentication, postal tracking, transactionalprinting, and other applications. For all of these applications, it iscommonly required that the system exhibit system reliability, good codereadability and durability.

BRIEF SUMMARY OF THE INVENTION

The present disclosure relates to the use of ink containing luminescentdyes for security applications.

In one aspect, method of printing a security code on an article includesapplying droplets of an ink composition with an ink jet printer to asurface of an article to print an encrypted code. The ink compositionincludes an organic solvent, a binder resin, and a luminescent dye.

In another aspect, an ink jet ink composition includes an organicsolvent; a solubilising agent selected from cyclic ketones, heterocyclicamides, cyclic alcohols, and furans; a binder resin; and a luminescentdye.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the initial solid state fluorescence ofExamples 1 and 2.

FIG. 2 is a graph showing the ΔE difference after fadometer exposure forvarious Blue Wool Scale reference standards.

DETAILED DESCRIPTION OF THE INVENTION

The disclosure relates to a process for printing and authenticating asecurity feature directly onto a good on a production line using acontinuous inkjet printer. The method includes providing a printer,printing onto the good using an ink with a prescribed formulation,optionally verifying the printed code immediately after printing, andsubsequently verifying the printed code after printing. The disclosedinks are visibly luminescent using excitation light in the UV or visibleranges. The printed code may be visible or invisible to the naked eye,but are readable by a machine vision system. The printed codes may bealphanumeric codes or barcode symbologies such as a linear or twodimensional barcodes. The data contained therein may be encrypted andtherefore may require special software to read and verify. The securityof the printed code is achieved through the combination of the highreadability of the fluorescent ink, the encryption of the data, and theuse of a special reader that both reads the fluorescent mark and decodesthe data. The printed codes can predictably last on products over thetypical lifetime of the product, for example, for one year or longer.The CU printer and prescribed inks will not cause undue productiondowntime for customers using the system.

In one embodiment, the printed marks provide a way for agencies tocontrol whether or not a tax has been assessed. For example, only goodsthat are marked by the methods described herein (thereby confirming thatthey meet taxation standards) would be authorized to be distributedthrough a wholesale or retail network. A system as prescribed herein isespecially important for high values items like tobacco and alcoholbased products for which relatively high levels of taxes are levied. Itis very important that the system be easy to adopt for variousproducers. Government mandated implementation of a system that reducesproduction efficiency would be very difficult to justify, sustain andultimately enforce. Hence, a printing and authentication system withhigh uptime and ease of integration is desired. Beverage production linespeeds can be several hundred feet per minute (FPM) up to about 1200 FPMon beer cans. The inks disclosed herein are dye based which provideadvantages over pigmented inks with respect to system uptime reliabilityand ease of maintenance. Good print quality that is important forreliable code verification is reliably maintained at these line speeds.The marks may be applied to any part of the packaging, are relativelywater and lightfast, and have good adhesion on the packaging. The marksare preferably at least partly visible over the substrate's backgroundso that the government agency and distributors/retailers can see themark without always having to use the special reader.

The printing and verification method occurs with minimal invasiveness toexisting production processes. A specific example of the kind of productthat would benefit by the current invention would be mass producedbeverages, such as beer. In most beer breweries, date and lot codes areapplied via some method of digital printing. Typically beer bottles arefilled with refrigerated beer (cold filled) and then subsequentlydigitally printed. Embodiments of the security marks disclosed hereinare intended to be applied on the same production line that thisprinting occurs, e.g., after the cold filling process. The marks thusproduced must be generally resistant to water and condensation, to whichthese consumer products are routinely exposed during and after thisprocess.

The mark may be applied to any surface of the product, top, side orunderside. A particularly suitable substrate on bottles onto which toapply the mark is the bottle cap. Caps are flat and present a consistentfocal plane for the reading system. Hence, a preferred process comprisessecurity marking after the bottles are filled and the caps are affixed.An alternative preferred cap printing process would be to mark the capsjust prior to the point when they are affixed. An example of a differentprint location would be the underside of a bottle or can, which also canbe a relatively flat surface (for example, at the center of the bottomof the can).

A suitable printer for printing the ink compositions described herein isa single nozzle continuous inkjet (CIJ) printer. CIJ printers candeliver printed marks at production line speeds and can be flexiblyarranged on a production line due to their compact overall size. Aparticularly suitable printer is a Videojet 1000 Series CIJ printer suchas the Videojet 1610 which has a number of known system advantages suchas high printer uptime, good print quality, and ease of maintenance.

Uptime in CIJ printers is generally limited by both short term and longterm maintenance requirements. Ink will slowly accumulate within theprint head due to, for example, the presence of unmerged satellites,micro-satellites, or a partly restricted nozzle orifice that can lead tojet skewing. The print head must be cleaned routinely with a cleaner bya production line operator. The rate of ink buildup can be particularlybad if the ink stream becomes skewed due to impurities in the ink or ifcomponents with low solubility get trapped in the nozzle duringoperation. The average period between routine print head cleanings isexpected to be on the order of days or weeks. Besides these routinecleanings, the ink systems used to recirculate the ink within theprinter will need to be repaired or replaced after a certain operationalperiod. The dye based inks described here would enable users to haveboth reduced downtime as a result of fewer routine print head cleaningsand reduced frequency of replacing ink system components within theprinter.

The marks may be applied at any reasonable production line speed, i.e.,less than 1200 FPM. In the bottling line example, marks may be appliedat line speeds around 500 FPM. The mark may be visible or invisible tothe unaided eye.

The inks preferably fluoresce in the visible range using excitationlight either in the UV or visible ranges. It is generally preferred thatmarking and reading occur very close in time (or location) on theproduction line. The overall security system can require that eachprinted mark is positively verified online. A potential scheme thatwould be used to accomplish this would be to assign each printed producta number (i.e., serialized, random or encrypted) that is embedded intothe printed security mark. These numbers may be generated by the printeror be fed to the printer via a network connection by, for example, acentralized database. An online vision system is used for verificationof each code that is printed. The verifier is fed the series of codesthat are printed and then attempts to match these with the actualprinted codes that it deciphers. As long as all of the deciphered codesmatch the sequence in the database, then the system continuesproduction. If a code is unreadable or missing, the system can bestopped to be checked and/or repaired. In this manner, insurance isprovided that each product is successfully marked.

Alternatively, only parts of the printed marks may be authenticated toensure that the mark has been printed, but not necessarily to extractall or even some of the data in barcode. For example, to ensure that theprinted mark is present, a reader may only need to determine that acompound with a specific fluorescence emission profile is present. Areader may look for an emission at a specified wavelength window whereemission would not normally occur without the intended security mark orwhere any light reflections would be attenuated to a suitable degree notto cause a false-positive. To assist in reading, the light source may befiltered to only emit at discrete wavelengths or the reader may beconfigured with filters to block unwanted reflected or incident light.

The marks may be alphanumeric or symbolical such as a linear or twodimensional barcode. The data contained therein may be easily encryptedby any means of encryption. Encryption is typically used to ensure thatcounterfeiters can not reproduce marks that contain the correctinformation (e.g., a code that corresponds to a given product type ormanufacturing origin), as the intent with any encryption scheme is torender the encryption pattern indecipherable to third parties.

The system may comprise any reading system capable of capturing theprinted image. For example a camera employing an imaging detector basedon a charged coupled device (CCD) or a complementarymetal-oxide-semiconductor (CMOS) may be employed. A specificnon-limiting example is a Cognex Legend camera. The illumination lightsource can be any suitable source but is typically one with an energyrange between about 200 and 450 nm. The particular source may beselected based on the absorption wavelength of the fluorescent dyes orthe required fluorescence emission, workplace, safety, or system cost.Preferred light sources are fluorescent mercury containing lamps orxenon flash lamps with relatively high output near either 250 or 360 nmwavelengths, although these discrete wavelengths should not be viewed aslimiting. Other preferred sources would include lamps employing lightemitting diodes with a center, discrete wavelength between about 350 and460 nm. To read at high speeds, image acquisition of the security markfor each marked product may need to occur on the order of 10milliseconds or less, or preferably 1 millisecond or less.

The CIJ ink formulation for printing the security mark generallycontains one or more luminescent compounds (or dyes), a resin, aconductive agent and a carrier solvent or solvent mixture. The inkformulation may further contain one or more co-resins and otheradditives such as surfactants, plasticizers, or solubilizing agents.

Suitable carrier solvents are fast-drying organic solvents. Particularlysuitable ones are ketones and alcohols with evaporation rate ratiosrelative to n-butyl acetate of greater than 1.0. The ink composition mayinclude the carrier solvent in a range of 60% to 90% by weight of theink composition, preferably in the range of 70% to 80% by weight.

The luminescent compound or dye is any compound that is soluble in thecarrier solvent to an extent that provides measurable fluorescence insolution and to an extent characterized by a weight formulationpercentage that is greater than 0.01%. Luminescent compounds may befluorescent, phosphorescent, bioluminescent, or the like and areselected from the following general classes: aromatic (e.g.,anthracene); substituted aromatic (e.g., nitrobenzene); heterocyclic(e.g., furan, thiophene); cyanine; phthalocyanine; naphthalocyanine;xanthene (e.g., fluorescein, rhodamine); acridine (e.g., euchrysine);phenazine (e.g., safranin); napthol; porphyrin; coumarin; pyrromethene;oxazine; oxazole (e.g., benzooxazole), perylene, napthalimide, triazine,imidazoline, di/triazole, stilbene (e.g., biphenystilbene) and anycombination thereof. Applicable luminescent compounds are any thatpossess a luminescence emission peak wavelength between 400 and 750 nm.

In one embodiment, the ink composition includes one or more invisiblefluorescent compounds with fluorescence in the violet, blue or greenregions of the light spectrum. Particularly suitable kinds of invisiblefluorescent compounds are optical brightener including oil solublevarieties such as benzoxazoles. One specific example is2,2′-(2,5-Thiophenediyl)bis[5-tert-butylbenzoxazole] with a CAS numberof 7128-64-5, sold under the trade name such as Uvitex OB, and TinopalOB. This compound is often used as a tracer compound in oily media (suchas fuels, pesicides, etc.) as it is hydrophobic and possesses goodsolubility in selected polar organic solvents like MEK.

A particularly suitable xanthene fluorescent dye used as a luminescentcompound conforms to the structure for C.I. Index Basic Red 11:1 and issold under the trade name Basonyl Red 560. Another suitable dye exampleis C.I Index Solvent Red 49. Other preferred luminescent compounds arefluorescent naphthalimide and perylene dyes sold under the trade nameLumogen from BASF Corporation. One particularly suitable example isPerylene F Red 300 (or 305). Other examples of preferred Perylene dyesare trade named Lumogen F Yellown 083, Lumogen F Yellow 170, Lumogen FOrange 240, Lumogen F Pink 285, Lumogen F Violet 570, and Lumogen F Blue650.

General structures of suitable perylene luminescent compounds are shownin the formulas below and are perylene diimides (Formula A) or perylenedianhydrides (Formula B) where R¹ and R² on the perylene rings and imidenitrogen, respectively, are hydrogen or alternatively, any conceivablesubstituents including those -alkyl, -aryl, -benzyl, -alkoxy or phenoxytypes as shown (provided only as examples). More examples of thisluminescent compounds include but are not limited to the followingformulations (or CAS#'s): 1,6,7,12-tetrachloroperylene tetracarboxylicacid dianhydride (CAS 156028-26-1);1,6,7,12-tetra-t-butylphenoxy-N—N′-dioctyl-perylene-3,4,9,10-tetracarboxylicdianhydride (CAS 872005-48-6);1,6,7,12-tetra-t-butylphenoxy-N—N′-bis(octadecyl)-perylene-3,4,9,10-tetracarboxylicdianhydride (CAS 545387-15-3);1,6,7,12-tetra(morpholinyl)-N,N′-bis(octadecyl)-3,4,9,10-perylenedicarbonyl amide;1,6,7,12-tetrachloro-N—N′-bis(octadecyl)-perylene-3,4,9,10-tetracarboxylicacid diimide (CAS 97097-95-5);1,6,7,12-tetra-t-butylphenoxy-N—N′-dioctyl-perylene-3,4,9,10-tetracarboxylicdiiimide (CAS 112100-07-9);1,6,7,12-tetrachloro-N—N′-dioctyl-perylene-3,4,9,10-tetracarboxylic aciddiimide (CAS 95689-65-5);1,6,7,12-tetra-t-butylphenoxy-N—N′-bis(octadecyl)-perylene-3,4,9,10-tetracarboxylicdianhydride (CAS 112100-07-9);N,N′-Bis(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxdiimide;Anthra[2,1,9-def:6,5,10-d′e′f]diisoquinoline-1,3,8,10(2H,9H)-tetrone,2,9-bis[2,6-bis(1-methylethyl)phenyl]-5,6,12,13-tetraphenoxy; CAS112100-07-9; and,N,N′-Bis(2,6-diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic diimide(CAS 82953-57-9).

Typically suitable luminescent compounds are fluorescent dyes withquantum yields in a given solvent with respect to a quantum yields ofstandard dyes equal to or better than 0.6. In general, the dyesspecified above exhibit quantum yields much greater than 0.5.

In preferred embodiments, a combination of two or more luminescentcompounds is used with different luminescence emission profiles. Forexample, the fluorescence peak emission of Species 1 will be a firstwavelength and the peak emission of Species 2 will be at a secondwavelength, wherein the first and second wavelengths are separated by atleast 50 nm. It is also preferred that the peak emission wavelength ofSpecies 1 is within 150 nm of the peak absorption wavelength of Species2.

Any combination of two or more of the luminescent compounds disclosedhereon may be used. In addition, non-luminescent colorants such astitanium dioxide and colored or black solvent dyes such as C.I. SolventBlack 29 can be added to the ink to impart additional visibility to thenaked eye.

The printed mark is preferably water resistant when printed on porousmaterials like paper and also nonporous materials like plastics ormetals. By water resistant is meant that within 1 minute after printingthe mark, it will resist removal from marked surface. For example, amark printed on a bottle cap, glass or aluminum, when submerged directlyin water 1 minute after printing, will exhibit no measurable loss influorescence intensity after a period of 1 hour, based on the measuredfluorescence intensity of the dried mark at one minute Such a printedmarked will also resist loss of intensity even if rubbed by a finger.

The printed code is also preferably lightfast when printed on non-poroussubstrates. Lightfastness is defined based on performance in testequipment meant to simulate either indoor or outdoor light exposure. Atypical simulated outdoor lightfastness test is conducted in an aircooled Xenon fadometer. The methods and apparatus generally conform tothose which are generally described in ASTM Methods G 151 and G154. In atypical outdoor simulation, the printed samples are exposed in the Xenonfadometer for a minimum continuous period of 48 hours at the followingtest conditions: 0.28 W/(m²-nm) irradiance at 340 nm; 40° C. black paneltemperature, and 40% Relative Humidity. The irradiance intensity shouldbe benchmarked against accepted Blue Wool Scale reference samples asdescribed for example in ISO 105 B02. After exposure to a givenradiation dosage, the color changes of Blue Wool samples can be assessedusing CIELAB ΔE measures. A ΔE color change lower than about 4 indicatesthat a given exposed Blue Wool standard is not overly faded. In otherwords, by finding samples that exhibit a ΔE lower than 4 at 48 hours ofexposure at the above described conditions, the relative Blue Woolrating for this exposure level can be established. If the fluorescentsamples are still readable at this interval, they are said to becomparable to the Blue Wool standards (i.e., the one with the lowest BWSrating and also a ΔE<4). After such a test on non-porous substrates(i.e., epoxy coated bottle caps and aluminum), the security marksdescribed herein are still readable using the systems and methodsdescribed herein. They also exhibit Blue Wool Scale ratings (as definedhere) of at least 3, or more preferably at least 4. This is very goodperformance for a dye based ink and is comparable to fluorescentpigmented inks that typically exhibit much lower initial fluorescenceintensities. The marks may also be readable at after periods that yieldeven higher net exposure energies than those defined above.

It is often the case that fluorescent compounds, particularly ones withhigh lightfastness, exhibit limited solubility in the preferred solventsdue in part to their molecular structure. Limited solubility of inkcomponents may result in reduced uptime even for a dye based CIJ inkjetprinter as described above. For example, a compound with low solubilitymay precipitate within or near the nozzle due to drying of solventaround the nozzle orifice. Further, as drops are generated by thesystem, the ink that is recirculated within the system is concentratedby evaporation further reducing solubility. Poor solubilization withinthe ink is further aggravated at low ambient temperatures though it isexpected that industrial inkjet printing systems must still operatereliably.

For consistent operation, a compound should be fully soluble in the inkformulation. Solubilising agents may be added in levels up to about 40%to provide sufficient solubility. Solubilising agents are defined assolvents that are slower drying than the volatile solvents that providesthe main ink solvent, and also show as good or better bulksolubilization of the luminescent compounds in terms of mass percentageof the luminescent compound that is soluble in the agent between about20 and 25° C. Suitable solubilising agents are cyclic ketones includingcyclohexanone; heterocyclic amides including alkylated pyrrolidones(i.e., n-methyl pyrrolidone, n-ethyl-pyrrolidone, 2-pyrrolidone,octylpyrrolidone); cyclic alcohols including benzyl alcohol, and furans.Solubilising agents may be aromatic or aliphatic.

The ink further includes binding agents, preferably water insolubleones. A binding agent may be defined as a resin with a softening pointgreater than 45° C. Suitable binders are any thermoplastic resins thatare soluble in the main carrier solvents. In an embodiment, the inkcomposition includes one or more resins selected from acrylic resins,vinyl chloride/vinyl acetate copolymers, polyesters; polyvinyl butyralresins, ethyl cellulose resins, polyurethane resins, modified rosinresins, phenolic resins, polyamide resins, cellulose ester resins,cellulose nitrate resins, polymaleic anhydride resins, acetal polymers,styrene acrylic copolymers, aldehyde resins, copolymers of styrene andallyl alcohols, epoxies, polyhydroxystyrenes and polyketone resins, andany combination thereof. Particularly suitable binders are selected fromthe classes of acrylics, polyesters, polyketones, silicones(polysiloxane), and cellulose esters.

Specific preferred acrylic polymers may be co- or terpolymers derivedfrom one or more alkyl-type monomers (such as a methyl methacrylate,n-butyl methacrylate, etc.) and a functionalized monomer such as acrylicacid or methacrylic acid. Examples of suitable resins are those from DowChemical Corporation sold under the trade-name Acryloid or Paraloid orDianal resins from Dianal Corporation. A specific example of anon-functionalized resin is sold under the trade name Paraloid B-60which is a methyl methacrylate and butyl methacrylate copolymer with amolecular weight of approximately 50,000 Daltons. Other acrylic polymersare potentially suitable such as ones Paraloids B-99n and B-66, whichare both copolymers of methyl methacrylate and butyl methacrylate andmay comprise small amounts of methacrylic acid. Still more examples thatare potentially suitable are available from Lucite Corporation under thetrade name Elvacite, such as Elvacite 2042, an ethyl methacrylatederivative.

Any suitable cellulosic resin can be employed, for example, a celluloseester or an alkylcellulose. Cellulose ester is cellulose some or all ofwhose hydroxyl groups have been modified to have an ester function ormixed ester functions, e.g., by one or more ester groups wherein theester group has 2-8 carbon atoms, preferably 2-5 carbon atoms. Examplesof cellulose ester include cellulose mixed esters such as acetatebutyrate and cellulose acetate propionate. An example of a suitablecellulose ester is cellulose acetate butyrate available commercially asCAB 551-0.01 from Eastman Chemical, Kingsport, Tenn. The alkylcelluloseis cellulose some or all of whose hydroxyl groups have been modified tocontain an alkyl group of 1-8 carbon atoms, preferably 2-4 carbon atoms,e.g., ethylcellulose. Nitrocellulose can also be employed as acellulosic resin. A preferred silicone resin includes a polysiloxanebackbone with any practical combination of substituents on the siliconeatoms such as 100% phenyl, 100% methyl blend of the two in anyproportion. An example of a mixed phenyl/methyl siloxane that ispreferred is sold with the trade name DC-233 from Dow Corning.

Preferred polysters are of the synthetic saturated variety for exampleas the result of a copolymerization of a diacid and a dialcohol.Specific preferred examples of such polyesters with good ketonesolubility are available from Evonik Industries under the trade name AddBond LTH or from Bayer Corporation under the trade name Desmophen5-105-10.

The exemplary resins above are each characterized by low molecularweights less than about 120,000 Daltons and very low acid numbers lessthan about 60.

More than one water insoluble binder may be employed. If multiple kindsof binders are used, the preferred percentage of water insoluble binderresin with respect to cumulative binder content is at least 60% and morepreferably greater than 90%. The cumulative binder concentration in theformulation is preferably no less than 5%, more preferably no less than10% and most preferably no less than 15%.

The ink composition preferably has a low solution resistivity, such aswithin the range of about 20 to about 2000 ohm-cm. The desiredresistivity can be achieved by the addition of an ionizable material orconductive agent which acts as a charge carrier in the liquid ink.Examples of such conductive agents include ammonium, alkali, andalkaline earth metal salts such as lithium nitrate, lithium thiocyanate,lithium trifluoromethanesulfonate, potassium bromide, and the like;amine salts such as dimethylamine hydrochloride, and hydroxylaminehydrochloride; tetraalkylammonium salts such as tetrabutylammoniumbromide, tetrabutylammonium hexafluorophosphate, tetrabutylammoniumthiocyanate, tetrapropylammonium bromide, tetrapropylammonium acetate,tetraphenylphosphonium bromide as well as ammonium acetate. Preferredconductive agents include lithium triflate, tetrabutylammoniumhexafluorophosphate, tetrabutylammonium nitrate, tetrabutylammoniumthiocyanate and tetrapropylammonium acetate. Any suitable amount of theconductive agents can be used. Normally, a conductive agent content ofup to about 3% by weight of the ink composition provides the desiredconductivity, typically in a range of about 0.5% to about 2%. In certaindesired ink compositions, high solution conductivity is not necessary,and the conductive agent may be omitted.

The ink composition may further include one or more additives such asplasticizers, surfactants, adhesion promoters, and mixtures thereof.Plasticizers may be polymeric and may be added in addition to a binderresin present, generally exhibiting molecular weights that are less than5,000. Examples of suitable plasticizers include phthalate plasticizers,e.g., alkyl benzyl phthalates, butyl benzyl phthalate, dioctylphthalate, diisobutyl phthalate, dicyclohexyl phthalate, diethylphthalate, dimethyl isophthalate, dibutyl phthalate, and dimethylphthalate, esters such as di-(2-ethylhexy)-adipate, diisobutyl adipate,glycerol tribenzoate, sucrose benzoate, dibutyl sebacate, dibutylmaleate, polypropylene glycol dibenzoate, neopentyl glycol dibenzoate,dibutyl sebacate, and tri-n-hexyltrimellitate, phosphates such astricresyl phosphate, dibutyl phosphate, triethyl citrate, tributylcitrate, acetyl tri-n-butyl citrate, polyurethanes, acrylic polymers,lactates, oxidized oils such as epoxidized soybean oil, oxidized linseedoil, and sulfonamide plasticizers such as Plasticizer 8, available fromMonsanto Co., St. Louis, Mo., which is n-ethyl o,p-toluene sulfonamide.

In certain embodiments, the plasticizer can be present in an amount fromabout 0 to about 5.0%, preferably from about 0.1 to about 2.5%, and morepreferably from about 0.25 to about 1.0% by weight of the inkcomposition.

Examples of surfactants include siloxanes, silicones, silanols,polyoxyalkyleneamines, propoxylated (poly(oxypropylene))diamines, alkylether amines, nonyl phenol ethoxylates, ethoxylated fatty amines,quaternized copolymers of vinylpyrrolidone and dimethyl aminoethylmethacrylate, alkoxylated ethylenediamines, polyethylene oxides,polyoxyalkylene polyalkylene polyamines amines, polyoxyalkylenepolyalkylene polyimines, alkyl phosphate ethoxylate mixtures,polyoxyalkylene derivatives of propylene glycol, and polyoxyethylatedfatty alcohols, fluorinated surfactants. Examples of a suitablepolymeric silicone based surfactant are sold under the trade nameSilwet. Examples of fluorinated surfactants include those sold under thetrade name Zonyl from Dupont Corporation.

In any of the embodiments, the surfactant additive may be present in anamount from about 0.001 to about 2.0% by weight, preferably from about0.005 to about 0.5% by weight of the ink composition.

The ink composition may have any suitable viscosity or surface tension.In embodiments the ink composition has a viscosity in the range of 1 cPto 10 cP, preferably in the range of 2 cP to 7 cP at 25° C. The inkcomposition preferably has a viscosity of between 2.5 and 5.0 at 25° C.The ink composition preferably has a surface tension from about 20 toabout 35 mN/m at 25° C.

The ink composition can be prepared by any suitable method. For example,the chosen ingredients can be combined and mixed with adequate stirringand the resulting fluid filtered to remove any undissolved impurities.

EXAMPLES Examples 1 to 3

An example of the limited solubility of a preferred luminescent compoundis shown. MEK is a preferred solvent for CIJ ink compositions because ofits wetting and drying characteristics as well as good solvency forpreferred binder resins and conductive agents. However, the solubilityof a preferred optical brightener, Tinopal OB, is limited in 100% MEK.Several different solvents were tested by added a specific weightpercentage of Tinopal OB to a given solvent or solvent blend. The datain Table 1 illustrate that by combining selected solubilizing agentswith MEK, the solubility of Tinopal OB in the blend is increased.

TABLE 1 Weight percentage of Tinopal OB SOLVENT 1% 2% 3% 5% MEK ✓ X X Xcyclohexanone ✓ ✓ ✓ X benzyl Alcohol ✓ ✓ X X n-Methyl pyrrolidone ✓ ✓ ✓X 50:50 ✓ ✓ X X Cyclohexanone:MEK ✓ = full soluble, no solid visible; X= partly or insoluble (in actual or by inference).

In this case, blends particularly with cyclohexanone and MEK can resultin increased solubility than with MEK alone. Formulations employingsolubilizing agents are provided in the following examples.

TABLE 2 Example 1 Example 3 Weight Example 2 Weight percentage Weightpercentage percentage MEK 74.76 74.76 81.28 Benzyl Alcohol 2.81 2.81Ethanol, denatured 4.00 Cyclohexanone 4.70 4.70 Paraloid B-66 16.2416.24 12.00 FC-122 2.00 TBAPF₆ 0.77 0.77 Tinopal OB 0.50 0.50 0.50Basonyl Red 560 0.20 0.20 0.20 Lumogen Red 305 0.50 Silwet L-7622 0.020.02 0.02 Total % 100.00 100.50 100.00 MEK is methyl ethyl ketoneavailable from Ashland Chemical Corporation. Cyclohexanone is availablefrom DSM Chemical Corporation. Benzyl alcohol is available from VesicolChemical Corporation. Ethanol, denatured is a proprietary grade ofdenatured ethanol containing less than 10% denaturants. TBAPF₆ istetrabutylammonium hexafluorophosphate available from Sigma AldrichCorporation. Paraloid B-66 is a thermoplastic acrylic resin availablefrom Dow Chemical Corporation. FC-122 is a lithium triflate availablefrom Ozark Fluorine Specialties Corporation. Silwet L-7622 is availablefrom Momentive Performance Material Corporation. Tinopal OB also knownas Uvitex OB and Basonyl Red 560 are available from BASF Corporation.Lumogen Red 305 is a perylene based fluorescent dye also from BASFCorporation.

In these formulation examples, Tinopal OB serves to absorb the lightenergy from the excitation source between about 300 and 420 nm Withoutintending to be bound to theory, one potential mechanism is that theTinopal OB fluoresces in the blue region between about 420 and 470 nm.The fluorescent light is then absorbed by the Basonyl Red 560 generatingthe excited state for that compound and subsequent orange/redfluorescence. The result is that the ink, when printed and excited withUV energy between about 250 and 450 nm, emits a very bright red/orangelight, depicted in FIG. 1 as the emitted light spectrum, which can thenbe read using a CCD camera sensitive to visible light in that energyrange. Alternatively, the printed mark may be excited by a visible lightsource. A UV light source is preferred as it provides better energeticseparation between the excitation light source and the emitted light.This in turn improves the printed symbol's contrast level as viewed bythe camera because light filters may be employed that effectivelyattenuate the source, but that do no greatly attenuate the emitted lightby the fluorophore.

As a demonstration, two dimensional data matrix barcodes were generatedusing a Videojet 1510 CIJ printer onto beer bottle caps. The caps werepassed beneath the print head via a moving transport at approximately200 FPM. Shortly after printing the data matrix codes were read with acamera based vision system (Cognex Legend camera) and an ultravioletfluorescent illumination lamp. In this particular instance, a 590 mmbandpass filter (BP 590) was used affixed on a 25 mm lens. Ninedifferent kinds of beer caps with highly variable colored pre-printedbackground graphic logos were printed and successfully read as is shownin the following Table 3. The data matrix codes were sufficientlyvisible to the camera irrespective of the color, darkness or variablenature of the pre-printed graphics.

TABLE 3 CODE READ CAP BACKGROUND COLORS GRADE Cap 1 white/gray A Cap 2red/gold A Cap 3 blue/white A Cap 4 blue/white A Cap 5 silver/gray A Cap6 black/gold A Cap 7 black/gold A Cap 8 white A Cap 9 gray/white A

For each successful read, the camera-based image acquisition time wasvery short (under 5 milliseconds) which demonstrates that thefluorescent images described here yield sufficient brightness to becamera to be visible at high production line speeds up to about 1200FPM. The acquisition time or shutter open time and code symbology wouldneed to be adjusted accordingly for a given line speed.

The printed security marks are sufficiently lightfast to last on thecaps (or other kinds of printed products) over the desired productlifetime. In this example, the products were expected to be stored up toone year in a warehouse or consumer store. Two dimensional barcodes wereprinted onto four different varieties of bottle caps using the ink ofExample 1. The printed codes were exposed in a fadometer at anirradiance level of 0.28 W/(m²-nm) (measured at the 340 nm referencepoint). All codes remained readable after 48 hours and after 72 hours ofexposure time. Codes of Example inks 1 and 2 were further printed onaluminum and also assessed by the reader after 48 hours exposure underthe same irradiance conditions. Very little or no loss in cameracontrast or readability was observed for these samples. In addition,Blue Wool Scale fabric standards of different ratings were exposed underthe same conditions. FIG. 2 depicts graphically the ΔE of the differentstandards at different exposure times. As can be seen, standards with aBWS rating of 3 are clearly faded under these conditions and those witha BWS rating of 4 or 5 are very close to exceeding the threshold of a ΔEof 4. The inks are still very readable at that time threshold. Hence,depending on the substrate, the printed inks exhibit lightfastnessratings equal to or better than textile standards with a BWS of 3.

The ink of Example 1 was operated in a Videojet 1510 printer for anextended period of time monitoring the code quality periodically. Theink provided generally very good print quality printing 2-D data matrixcodes onto beer bottle caps. The ink was printed repeatedly into areceptacle for over 233 hours at 45° C. ambient temperature. During thisperiod, the printer required three routine print head cleanings with acalculated average time of 77 hours between failures. Example 3 ink wassimilarly run in the same printer at the same conditions for 226 hoursrequiring four routine cleanings yielding a run average of 57 hours. Inseparate tests, the inks were also operated at low temperature (5° C.)where it was expected that the relatively poor solubility of thefluorescent brightener in the carrier solvent at low temperatures mightnegatively impact reliability. The ink of Example 1 employingsolubilizing agents was operated for a period of more than 300 hourswithout failure or the need for a routine cleaning. In comparison, theink of Example 3 was operated for only about 116 hours and yet requiringfive routine cleanings with a resulting average run time of only 23hours. The primary difference between the two formulations was thatExample 1 employed the solubilizing agents benzyl alcohol andcyclohexanone while Example 2 employed none. Hence, it was deduced thatsolubilizing agents dramatically increase the average run time of theinks, particularly at low ambient temperatures.

Examples 4-7

Additional suitable formulations are provided in the following examples.

TABLE 4 Example 4 Example 5 Example 6 Example 7 Weight Weight WeightWeight percentage percentage percentage percentage MEK 65.47 68.07 70.2156.49 Benzyl Alcohol 2.50 2.40 2.30 Ethanol, denatured 4.70 4.60 4.334.70 Cyclohexanone 4.70 4.60 4.33 10.50 Paraloid B-66 12.40 ParaloidB-99 19.70 CAB 551-0.01 10.14 Add Bond LTH 25.00 DC233 5.50 6.45 FC-1222.10 1.60 1.47 2.60 TBAPF₆ Tinopal OB 0.52 0.52 0.48 0.40 Solvent Red 490.31 0.31 0.29 0.31 Total % 100.00 100.00 100.00 100.00 Paraloid B-99 isa methacrylate base terpolymer available from Dow Chemical Corporation.CAB 551-0.01 is a cellulose ester from Eastman Chemical Corporation. AddBond LTH is a polyster resin available from Evonik IndustriesCorporation. DC233 is a polysiloxane resin available from Dow CorningCorporation. Solvent Red 49 is a solvent soluble xanthene dye availablefrom Sunbelt Corporation.

The Examples 4 through 7 each exhibited required properties for properjetting with a CU printer. A Videojet 1000 Series printer was used togenerate print samples of the inks on both bottle caps and aluminumplates as before. The relative lightfastness of the codes were assessed,this time using double the exposure intensity or 0.56 W/(m²-nm)(measured at the 340 nm reference point). The samples were all suitablylightfast, although readability varied slightly by ink. Thesecomparisons are set forth in Table 5. All printed samples also showedgood adhesion on metals, plastics and bottle caps as was necessary.

TABLE 5 Example 4 Example 5 Example 6 Example 7 Exposure time, hours 2424 24 24 % Codes readable 100 90 90 90 (all samples) Red dye fadingnoted on No fading No fading No fading Some caps fading Red dye fadingnoted on No fading No fading No fading No fading aluminum

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The invention claimed is:
 1. A method of printing a security code on anarticle comprising: applying droplets of an ink composition with an inkjet printer to a surface of an article to print an encrypted code,wherein the ink composition comprises: an organic solvent; a binderresin; and two or more luminescent dyes, wherein each luminescent dyehas a different luminescence emission profile, wherein the luminescentdyes comprise an invisible fluorescent dye that absorbs ultravioletlight and emits visible light, and one or more visible fluorescent dyesthat absorb the light emitted by the invisible fluorescent dye whereinthe luminescent dye is selected from the classes of aromatic,substituted aromatic, heterocyclic, cyanine, xanthene, acridine,phenazine, napthol, porphyrrin, coumarin, pyrromethene, oxazine,oxazole, perylene, and napthalimide dyes, and combinations thereof; anda solubilizing agent selected from cyclic ketones, cyclic alcohols,furans, and mixtures thereof.
 2. The method of claim 1 wherein theorganic solvent comprises a ketone, an alcohol, or a mixture thereof,and is present in an amount in a range of 60% to 90% by weight of theink composition.
 3. The method of claim 1 wherein the invisiblefluorescent dye absorbs ultraviolet light while emitting light in awavelength range between 400 and 550 nm, and the one or more visiblefluorescent dyes that absorbs light in a wavelength range between 400and 550 nm and emit light above 550 nm, wherein an emissive peak of theinvisible fluorescent dye is separated by at least 50 nm from anemissive peak of the visible fluorescent dye.
 4. The method of claim 1wherein the ink composition comprises an invisible fluorescent compound.5. The method of claim 1 wherein the code is an alphanumeric code. 6.The method of claim 1 wherein the code is a bar code.
 7. The method ofclaim 6 wherein the bar code is a two dimensional bar code.
 8. Themethod of claim 1 further comprising reading the code with a visionsystem.
 9. The method of claim 8 further comprising verifying theauthenticity of the code.
 10. The method of claim 1 wherein the code isvisible to the unaided eye.
 11. The method of claim 1 wherein the codeis invisible to the unaided eye.
 12. The method of claim 1 wherein thesolubilizing agent comprises cyclohexanone.
 13. The method of claim 1wherein the solubilizing agent is present in an amount up to 40% byweight of the ink composition.
 14. An ink jet ink compositioncomprising: an organic solvent, wherein the organic solvent comprises aketone, an alcohol, or a mixture thereof, and is present in an amount ina range of 60% to 90% by weight of the ink composition; a solubilizingagent selected from cyclic ketones, cyclic alcohols, and furans; abinder resin; and two or more different luminescent dyes, wherein eachluminescent dye has a different luminescence emission profile, whereinthe luminescent dyes comprise an invisible fluorescent dye that absorbsultraviolet light and emits visible light, and one or more visiblefluorescent dyes that absorb the light emitted by the invisiblefluorescent dye, wherein the luminescent dye is selected from theclasses of aromatic, substituted aromatic, heterocyclic, cyanine,xanthene, acridine, phenazine, napthol, porphyrrin, coumarin,pyrromethene, oxazine, oxazole, perylene, and napthalimide dyes, andcombinations thereof.
 15. The ink jet ink composition of claim 14further comprising an invisible fluorescent compound.
 16. The ink jetink composition of claim 15 wherein the invisible fluorescent compoundcomprises a benzoxazole.
 17. The ink jet ink composition of claim 14wherein the invisible fluorescent dye absorbs ultraviolet light whileemitting light in a wavelength range between 400 and 550 nm, and the oneor more visible fluorescent dyes that absorbs light in a wavelengthrange between 400 and 550 nm and emit light above 550 nm, wherein anemissive peak of the invisible fluorescent dye is separated by at least50 nm from an emissive peak of the visible fluorescent dye.
 18. The inkjet ink composition of claim 14 further comprising a conductive agent.19. The ink jet ink composition of claim 14 wherein the ink compositionprovides a light stable and water resistant mark when printed on asubstrate.
 20. The ink jet ink composition of claim 14 wherein thesolubilizing agent is selected from benzyl alcohol and cyclohexanone.21. The ink jet ink composition of claim 14 wherein the solubilizingagent comprises cyclohexanone.
 22. The ink jet ink composition of claim14 wherein the solubilizing agent is present in an amount up to 40% byweight of the ink composition.